Pterois fish in the Atlantic range from 5 to 45 cm (2.0 to 17.7 in) in length, weighing from 0.025 to 1.3 kg (0.055 to 2.866 lb).[2][7][8] They are well known for their ornate beauty, venomous spines, and unique tentacles.[9][10] Juvenile lionfish have a unique tentacle located above their eye sockets that varies in phenotype between species.[9] The evolution of this tentacle is suggested to serve to continually attract new prey; studies also suggest it plays a role in sexual selection.[9]

Pterois species can live from five to 15 years and have complex courtship and mating behaviors.[11] Females release two mucus-filled egg clusters frequently, which can contain as many as 15,000 eggs.[11][12] Studies on Pterois reproductive habits have increased significantly in the past decade.[12] All the species are aposematic: they have conspicuous coloration with boldly contrasting stripes and wide fans of projecting spines, advertising their ability to defend themselves.[13]

According to a study that involved the dissection of over 1,400 lionfish stomachs from Bahamian to North Carolinian waters, Pterois fish prey mostly on small fish, invertebrates, and mollusks in large amounts, with some specimens’ stomachs containing up to six different species of prey.[7] The amount of prey in lionfish stomachs over the course of a day suggests lionfish feed most actively from 7:00–11:00 a.m., and decrease feeding throughout the afternoon. Lionfish are skilled hunters, using specialized bilateral swim bladder muscles to provide precise control of location in the water column, allowing the fish to alter its center of gravity to better attack prey.[7] The lionfish then spreads its large pectoral fins and swallows its prey in a single motion.[11] They blow jets of water while approaching prey, apparently to disorient them.[14] In addition to confusing prey, these jets of water also alter the orientation of the prey so that the smaller fish is facing the lionfish. This results in a higher degree of predatory efficiency as head-first capture is easier for the lionfish.[15] (In general, when smaller fishes escape from possible danger, they do so against the current.)

Aside from instances of larger lionfish individuals engaging in cannibalism on smaller individuals, adult lionfish have few identified natural predators, likely from the effectiveness of their venomous spines. Moray eels (family Muraenidae),[16][17] bluespotted cornetfish (Fistularia commersonii), and large groupers, like the tiger grouper (Mycteroperca tigris)[18] and Nassau grouper (Epinephelus striatus), have been observed preying on lionfish.[19][20][21] It remains unknown, however, how commonly these predators prey on lionfish.[22] Sharks are also believed to be capable of preying on lionfish with no ill effects from their spines.[23] Park officials of the Roatan Marine Park in Honduras have attempted to train sharks to feed on lionfish as of 2011 in an attempt to control the invasive populations in the Caribbean.[24][25] The Bobbit worm, an ambush predator, has been filmed preying upon lionfish in Indonesia.[26] Predators of larvae and juvenile lionfish remain unknown, but may prove to be the primary limiting factor of lionfish populations in their native range.[17]

Lionfish are known for their venomous fin rays, an uncommon feature among marine fish in the East Coast coral reefs. The potency of their venom makes them excellent predators and hazardous to fishermen and divers.[2]Pteroisvenom produced negative inotropic and chronotropic effects when tested in both frog and clam hearts[28] and has a depressing effect on rabbit blood pressure.[29] These results are thought to be due to nitric oxide release.[10] In humans, Pterois venom can cause systemic effects such as extreme pain, nausea, vomiting, fever, breathing difficulties, convulsions, dizziness, redness on the affected area, headache, numbness, paresthesia (pins and needles), heartburn, diarrhea, and sweating. Rarely, such stings can cause temporary paralysis of the limbs, heart failure, and even death. Fatalities are common in very young children, the elderly, those with a weak immune system, or those who are allergic to their venom. Their venom is rarely fatal to healthy adults, but some species have enough venom to produce extreme discomfort for a period of several days. However, Pterois venom is a danger to allergic victims as they may experience anaphylaxis, a serious and often life-threatening condition that requires immediate emergency medical treatment. Severe allergic reactions to Pterois venom include chest pain, severe breathing difficulties, a drop in blood pressure, swelling of the tongue, sweating, runny nose, or slurred speech. Such reactions can be fatal if not treated. There is a possibility for a human to be stung without any venom being injected. If venom is injected, the sting will hurt more than just briefly. Lionfish are not aggressive towards swimmers. Most accidents happen to fishermen who happen to catch them.

The lionfish is a predator native to the Indo-Pacific. It aggressively preys on small fish and invertebrates. They can be found around the seaward edge of reefs and coral, in lagoons, and on rocky surfaces commonly to 50 m deep, although lionfish have on multiple occasions been recorded to 300 m depth.[31] They show a preference for turbid inshore areas and harbors,[32] and have a generally hostile attitude and are territorial towards other reef fish.[33] Many universities in the Indo-Pacific have documented reports of Pterois aggression towards divers and researchers.[33]P. volitans and P. miles are native to subtropical and tropical regions from southern Japan and southern Korea to the east coast of Australia, Indonesia, Micronesia, French Polynesia, and the South Pacific Ocean.[32]P. miles is also found in the Indian Ocean, from Sumatra to Sri Lanka and the Red Sea.

Two of the twelve species of Pterois, the red lionfish (P. volitans) and the common lionfish (P. miles), have established themselves as significant invasive species off the East Coast of the United States and in the Caribbean. About 93% of the invasive population in the Western Atlantic is P. volitans.[34] They have been described as "one of the most aggressively invasive species on the planet".[25]

The red lionfish is found off the East Coast and Gulf Coast of the United States and in the Caribbean Sea, and was likely first introduced off the Florida coast by the early to mid-1990s.[35] This introduction may have occurred in 1992 when Hurricane Andrew destroyed an aquarium in southern Florida, releasing six lionfish into Biscayne Bay.[36] However, a lionfish was discovered off the coast of Dania Beach, south Florida, as early as 1985, before Hurricane Andrew.[7][37][38] The lionfish resemble those of the Philippines, implicating the aquarium trade.[39] The lionfish may have been purposely discarded by unsatisfied aquarium enthusiasts.[39] This is in part because lionfish require an experienced aquarist, but are often sold to novices who find their care too difficult. In 2001, NOAA documented several sightings of lionfish off the coast of Florida, Georgia, South Carolina, North Carolina, Bermuda, and Delaware. In August 2014, when the Gulf Stream was discharging into the mouth of the Delaware Bay, two lionfish were caught by a surf fisherman off the ocean side shore of Cape Henlopen State Park: one red one that weighed 1 pound 4.5 ounces and one common one that weighed 1 pound 2 ounces. Three days later a 1-pound 3 ounce red lionfish was caught off the shore of Broadkill Beach which is in the Delaware Bay approximately 15 miles north of Cape Henlopen State Park. Lionfish were first detected in the Bahamas in 2004.[40] In June 2013 lionfish were discovered as far east as Barbados,[41] and as far south as the Los Roques Archipelago and many Venezuelan continental beaches.[42] Lionfish were first sighted in Brazilian waters in late 2014.[citation needed] Genetic testing on a single captured individual revealed that it was related to the populations found in the Caribbean, suggesting larval dispersal rather than an intentional release.[citation needed]

P. volitans is the most abundant species of the invasive lionfish population in the Atlantic and Caribbean.

Extreme temperatures present geographical constraints in the distribution of aquatic species,[47] indicating temperature tolerance plays a role in the lionfish’s survival, reproduction, and range of distribution.[40] The abrupt differences in water temperatures north and south of Cape Hatteras directly correlate with the abundance and distribution of Pterois.[47]Pterois expanded along the southeastern coast of the United States and occupied thermal-appropriate zones within 10 years,[47] and the shoreward expansion of this thermally appropriate habitat is expected in coming decades as winter water temperatures warm in response to anthropogenic climate change.[48] Although the timeline of observations points to the east coast of Florida as the initial source of the western Atlantic invasion, the relationship of the United States East Coast and Bahamian lionfish invasion is uncertain.[49] Lionfish can tolerate a minimum salinity of 5 parts per thousand and even withstand pulses of freshwater, which means they can also be found in estuaries of freshwater rivers.[50]

The lionfish invasion is considered to be one of the most serious recent threats to Caribbean and Florida coral reef ecosystems. To help address the pervasive problem, in 2015 National Oceanic and Atmospheric Administration (NOAA) partnered with the Gulf and Caribbean Fisheries Institute to set up a lionfish portal to provide scientifically accurate information on the invasion and its impacts.[51] The lionfish web portal[52] is aimed at all those involved and affected, including coastal managers, educators and the public and the portal was designed as a source of training videos, fact sheets, examples of management plans, and guidelines for monitoring. The web portal draws on the expertise of NOAA's own scientists as well as other scientists and policy makers from academia NGO and managers.[citation needed]

Lionfish have successfully pioneered the coastal waters of the Atlantic in less than a decade and pose a major threat to reef ecological systems in these areas. A study comparing their abundance from Florida to North Carolina with several species of groupers found they were second only to the native scamp grouper and equally abundant to the graysby, gag, and rock hind.[2] This could be due to a surplus of resource availability resulting from the overfishing of lionfish predators like grouper.[53] Although the lionfish has not expanded to a population size currently causing major ecological problems, their invasion in the United States coastal waters could lead to serious problems in the future. One likely ecological impact caused by Pterois could be their impact on prey population numbers by directly affecting food web relationships. This could ultimately lead to reef deterioration and could negatively influence Atlantic trophic cascade.[11] Lionfish have already been shown to overpopulate reef areas and display aggressive tendencies, forcing native species to move to waters where conditions might be less than desirable.[2]

Lionfish could be reducing Atlantic reef diversity by up to 80%.[33] In July 2011, lionfish were reported for the first time in the Flower Garden Banks National Marine Sanctuary off the coast of Louisiana.[54] Sanctuary officials said they believe the species will be a permanent fixture, but hope to monitor and possibly limit their presence.[citation needed]

Since lionfish thrive so well in the Atlantic and the Caribbean due to nutrient-rich waters and lack of predators, the species has spread tremendously. A single lionfish, located on a reef, reduced young juvenile reef fish populations by 79%.[55]

P. miles makes up about 7% of the invasive lionfish population in the Atlantic and Caribbean.

Red lionfish are an invasive species, yet relatively little is known about them. NOAA has research foci include investigating biotechnical solutions for control of the population, and understanding how the larvae are dispersed.[citation needed] Another important area of study is what controls the population in its native area. Researchers hope to discover what moderates lionfish populations in the Indo-Pacific and apply this information to control the invasive populations, without introducing additional invasive species.[citation needed]

Rigorous and repeated removal of lionfish from invaded waters could potentially control the exponential expansion of the lionfish in invaded waters.[2] A 2010 study showed effective maintenance would require the monthly harvest of at least 27% of the adult population. Because lionfish are able to reproduce monthly, this effort must be maintained throughout the entire year.[56]

Even to accomplish these numbers seems unlikely, but as populations of lionfish continue to grow throughout the Caribbean and Western Atlantic, actions are being taken to attempt to control the quickly growing numbers. In November 2010, for the first time the Florida Keys National Marine Sanctuary began licensing divers to kill lionfish inside the sanctuary in an attempt to eradicate the fish.[citation needed]

Conservation groups and community organizations in the Eastern United States have organized hunting expeditions for Pterois such as the Environment Education Foundation's ‘lionfish derby’ held annually in Florida.[44] Divemasters from Cozumel to the Honduran Bay Islands and at Reef Conservation International which operates in the Sapodilla Cayes Marine Reserve off Punta Gorda, Belize, now routinely spear them during dives.[citation needed] However, while diver culling removes lionfish from shallow reefs reducing their densities,[57] lionfish have widely been reported on mesophotic coral ecosystems (reefs from 30–150 m) in the western Atlantic[58] and even in deep-sea habitats (greater than 200 m depth).[31] Recent studies have suggested that the effects of culling are likely to be depth-specific, and so have limited impacts on these deeper reef populations.[59] Therefore other approaches such as trapping are advocated for removing lionfish from deeper reef habitats.[31][58][59]

Long-term culling has also been recorded to cause behavior changes in lionfish populations. For example, in the Bahamas, lionfish on heavily culled reefs have become more wary of divers and hide more within the reef structure during the day when culling occurs.[60] Similar lionfish responses to divers have been observed when comparing culled sites and sites without culling in Honduras, including altered lionfish behaviour on reefs too deep for regular culling, but adjacent to heavily culled sites potentially implying movement of individuals between depths.[59]

While culling by marine protection agencies and volunteer divers is an important element of control efforts, development of market-based approaches, which create commercial incentives for removals, has been seen as a means to sustain control efforts. The foremost of these market approaches is the promotion of lionfish as a food item.[61][62] Another is the use of lionfish spines, fins and tails for jewelry and other decorative items. Lionfish jewelry production initiatives are underway in Belize, the Bahamas and St. Vincent and the Grenadines.

In 2014 at Jardines de la Reina National Marine Park in Cuba, a diver experimented with spearing and feeding lionfish to sharks in an effort to teach them to seek out the fish as prey.[63] However, by 2016, Cuba was finding it more effective to fish for lionfish as food.[64]

In 2010, NOAA began a campaign to encourage the consumption of the fish.[44] The "Lionfish as Food" campaign encourages human hunting of the fish as the only form of control known to date. Encouraging the consumption of lionfish could not only help to maintain a reasonable population density, but also provide an alternative fishing source to overfished populations, such as grouper and snapper. NOAA also encourages people to report lionfish sightings, to help track lionfish population dispersal.[65] To promote the campaign, the Roman Catholic Church in Colombia agreed to have their clergy's sermons suggest to their parishioners (84% of the population) to eat the fish species on Fridays, Lent and Easter, which proved highly successful to decrease the invasive fish problem.[66]

When properly filleted, the naturally venomous fish is safe to eat. There has been some concern about the risk of ciguatera food poisoning (CFP) from consumption of lionfish, and the FDA included lionfish on the list of species at risk for CFP when lionfish are harvested in some areas tested positive for ciguatera. However, there have been no verified cases of CFP from consumption of lionfish, and published research has found that the toxins in lionfish venom may be causing false positives in tests for presence of ciguatera.[67] The Reef Environmental Education Foundation provides advice to restaurant chefs on how they can incorporate the fish into their menus. The NOAA calls the lionfish a "delicious, delicately flavored fish" similar in texture to grouper.[44] Recipes for lionfish include deep frying, ceviche, jerky, grilling, and sashimi.